PrivateMail is described as 'With Private-Mail, your email is kept private with unbreakable security that works with any OpenPGP compatible email client' and is an app in the Security & Privacy category. There are nine alternatives to PrivateMail for a variety of platforms, including Online / Web-based, Android, iPhone, iPad and Self-Hosted solutions. The best alternative is ProtonMail, which is both free and Open Source. Other great apps like PrivateMail are Tutanota (Freemium, Open Source), Posteo (Paid, Open Source), mailbox.org (Paid) and StartMail (Paid).
mailbox.org offers a secure e-mail account for home and business use. The domain name, email@example.com, is easy to remember and can be understood anywhere in the world. They have been operating e-mail accounts for more than 20 years and are a highly reliable service provider.
Tildamail is a free, decentralized, and secure email system, developed by Stanford graduates. We are an end-to-end encrypted email system that protects your privacy. Tilda is a standard for DApps backed by self-sovereign data. User data never touches our servers.
Countermail is a web-based email service. It is hosted in Sweden. Its focus is on privacy. It provides several features, such as PGP support and diskless servers to protect users ability to communicate securely and anonymously.